1. Field of the Invention
This invention relates to natural gas fuel supply for a vehicle engine and more particularly to a control module for controlling the feeding of gas between a fuel tank and the engine.
2. Description of the Related Art
The use of natural gas as a vehicle engine fuel has substantial environment benefits in that the exhaust emissions of an engine using such fuel are extremely low. Natural gas fuel, however, has low energy density which necessitates fuel storage in a vehicle in a highly compressed form to increase such density. This necessitates the regulation of the fuel pressure down to a lower value suitable for use in the vehicle combustion chamber. Due to this factor, the fuel supply system represents 60-90% of the cost of conversion of a vehicle to run on natural gas.
There are two fundamental requirements for a natural gas fuel supply system: 1. storing enough fuel to provide adequate travel range by compressing the fuel prior to its being fed into the fuel tank; 2. Regulating the compressed fuel down to a suitable pressure and temperature so that the air/fuel ratio can be controlled to achieve the required emissions and fuel economy objectives.
In prior art natural gas fuel supply systems such as described in U.S. Pat. No. 5,611,316 issued Mar. 18, 1997 to Oshima et al., the high pressure gas is fed through high pressure lines to the engine where the pressure is lowered and regulated by a suitable regulator and the feeding of the fuel controlled. In such prior art systems, the fuel line running between the gas tank and the engine and other related components must be able to handle the high pressure which necessitates the use of expensive materials such as stainless steel. Further, the feeding of the gas at high pressure presents the danger of leaks and evaporative emissions which could cause system breakdown along with the resultant hazards.